Psychological stress has long been implicated in the etiology of essential hypertension and sudden cardiac death. While attempts have been made to develop stress models of hypertension in animals, no behavioral studies have simultaneously assessed blood pressure and electrophysiological properties of the heart. This proposal seeks to examine both these variables during complex behavioral stressors in dogs and rats. In an attempt to maximize the effects of stress on cardiovascular function, the variables of predictability and controllability will be systematically evaluated. This model will be utilized since previous paradigms of behavioral stress which have been studied do not evoke permanent changes in blood pressure. During these manipulations, permanent coronary occlusions will be performed. Heart rhythms will be recorded and severity of arrhythmia noted. In addition, a number of cardiovascular variables will be monitored, including blood pressure, stroke volume cardiac output, heart rate, and total peripheral resistance. The goal of these investigations is to determine the kinds of behavioral intervention which most reliably alter cardiovascular function, so that future research can more specifically define the cardiovascular, biochemical and anatomical correlates of sudden cardiac death during psychological stress.